1. Field of the Invention
The present invention relates to a proton exchange membrane fuel cell, particularly to a sealing structure for sealing single fuel cell and stacked fuel cell module.
2. Description of the Prior Art
In the field of fuel cell technology, fuel cell is classified based on the electrolyte thereof. There are approximately five kinds of fuel cells which have been developed, namely, proton exchange membrane fuel cell or polymer electrolyte membrane fuel cell, abbreviated as PEMFC, alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC). Each kind of fuel cell has its own advantages, disadvantages and extent of applications. Among these known fuel cells, the PEMFC would be the most competitive power supply and has high practical value.
Principally, a fuel cell is combines hydrogen and oxygen in an electrochemical reactions to produce water and release electrical energy, which can be basically considered a device that is the reverse of water electrolysis.
The performance of fuel cell mainly depends on the extent of the electrochemical reaction, which is affected by the materials forming the layers of the fuel cell and the sealing between the plates. Hence, the selections of the materials and prevention of leakage between the layers will be the important factors of the performance of the fuel cell operations.
However, although much effort has been put to settle the aforesaid problems, the result is not satisfied. Generally speaking, there are two reasons adversely affecting the precise control: one is a failure to efficiently perform the leak and pollution proof functions between the anode and cathode bipolar plates, and the other is a failure to properly control the conductive compression pressure between each layer under an optimal status.
Please refer to FIG. 1 which shows a cross-sectional view of the single cell of a prior art PEMFC. As shown, the single cell is constituted by an anode plate 101 and a cathode plate 102. Basically, an anode gas diffusion layer 104 and a cathode gas diffusion layer 105 are separately provided on the two sides of a proton exchange membrane (PEM) 103, forming a membrane electrode assembly (MEA). The MEA is mounted between the anode plate 101 and the cathode plate 102.
The inner surface of the anode plate 101 facing the MEA is formed with a plurality of anode gas channels 101a, and the inner surface of the cathode plate 102 facing the MEA is formed with a plurality of cathode gas channels 102a. The anode plate 101 and cathode plate 102 are separately provided with gaskets 106, 107 along edge portions thereof. Then, the MEA is disposed on a central portion of the anode plate 101 and cathode plate 102, forming a gastight single cell.
Practically, a plurality of such single cells are stacked to configure a fuel cell stack as shown in FIG. 2. After the connections of plural manifolds or through holes adapted to supply gases and coolant and the dispositions of an upper end plate 108a and a lower end plate 108b, together with the conductive terminals 109a, 109b, the complete fuel cell stack 100 is able to perform the desired conductive reactions under a predetermined compression pressure by fastening a plurality of tie rods 110 therethrough.
However, this construction for the fuel cell will result in the following problems:                (1) The hydrogen supplied from the channels 101a of the anode plate 101 tends to leak out due to the gaps between the gasket 106 and the anode plate 101. Meanwhile, the oxygen or air supplied from the channels 102a of the cathode plate 102 also tends to leak out due to the gaps between the gasket 107 and the cathode plate 102. The leakage of hydrogen and oxygen significantly affects the electrochemical reactions of the fuel cell. This disadvantageous phenomenon will be extremely obvious after a considerable duration of using the gaskets 106, 107. Integral formation of those gaskets 106, 107 into a single gasket may improve the situation, but it cannot thoroughly solve the problem.        (2) Due to the property of the materials employed for the gaskets 106, 107 and the different aging rates of the gaskets, the compression pressure at the region of the gaskets is uneven, and hence the compression pressure in the whole fuel cell becomes uneven. This is why the reaction gases often fail to diffuse uniformly, which is a severe block to the conductivity of a PEMFC. Furthermore, because the whole PEMFC relies on the tie rods 110 disposed circumferentially to control its compression pressure, the pressure of the circumferential portion is significantly different from that of the central portion, which will adversely affect the operational effects of the fuel cell.        (3) Utilizing a gasket between the plates fails to efficiently isolate pollution and fails to properly locate each layer in position. Further, because it is difficult to control in advance the compression pressure at an optimal range, it is not possible to pre-prepare a stock of the single cells in the modulized form to proceed with any of the possible types of tests for the purposes of cost reduction and mass production. This is really the key factor of the failure to widely and effectively apply PEMFCs in the industry nowadays.        
Accordingly, to provide a highly efficient, mass-producible and cost-saving modulized single cell and cell module to solve the above-mentioned problems and further supply breakthrough ideas in manufacturing the PEMFC is a common desire of people skilled in this field.